1. Field of the Invention
The present invention relates to a radiation image capturing apparatus that includes a radiation detector for detecting a radiation image of a subject and generating electrical signals corresponding to the detected radiation image, and more particularly, to a radiation image capturing apparatus that includes a mechanism for cooling the radiation detector.
2. Description of the Related Art
In a radiation image capturing apparatus, such as an X-ray breast image capturing apparatus (e.g., mammography apparatus) or the like, a radiation image is generated by exposing a subject (patient) to radiation and recorded into a radiation image recording unit (i.e., a radiation detector). The radiation image recording unit is thereafter scanned with reading light emitted from a reading light source moved relative to the radiation image recording unit to allow readout of the information associated with the recorded radiation image. An example of such a radiation image capturing apparatus is disclosed in U.S. Pat. No. 6,268,614.
Examples of the radiation image recording unit that can be used in the above-mentioned apparatus include a radiation detector of electric readout type having a plurality of photoelectric conversion elements and devices such as thin-film transistors (TFT), CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensor, or a radiation detector of light readout type, direct conversion type, or indirect conversion type.
In such radiation image capturing apparatuses, it is necessary to maintain a proper temperature range because of constraints resulting from the temperature characteristics of the photoelectric conversion elements, the effects of thermal noise generated by the electrical circuit, and the like. Therefore, a radiation image capturing apparatus is provided with an air or water-type cooler. One example of such an apparatus is disclosed in Japanese Laid-Open Patent Publication No. 2000-037374.
The radiation image capturing apparatus disclosed in Japanese Laid-Open Patent Publication No. 2000-037374 is directed to effective cooling of the radiation detector. The radiation image capturing apparatus disclosed in the above-mentioned publication includes, as can be seen in FIG. 1 of the publication, a two-dimensional radiation detector 5 and a signal converter 6 contained in a housing 4 of an image capturing unit 3 in this order from the front of the housing 4. An upper portion of the housing 4 is provided with a fan 7, which serves as a cooling means, and a lower portion of the housing 4 is provided with an inlet port 4a for introducing outside air. Release of the heat generated by the two-dimensional radiation detector 5 is accomplished by actuating the fan 7 and thereby introducing air into the housing 4 through the inlet port 4a. 
In the apparatus disclosed in Japanese Laid-Open Patent Publication No. 2000-037374, the inlet port 4a is formed at one end of the radiation detector 5, while the fan 7 is located at the other end, so that cooling of the whole radiation detector can be achieved. In many radiation image capturing apparatuses, however, the arrangement of the radiation detector within the image capturing unit is restricted for various reasons. The image capturing unit of a mammography apparatus, for example, is required to be movable around the breast so that images of the breast from different directions can be captured. Consequently, a large size for the image capturing unit housing is not permitted, and the radiation detector has to be contained in a small space. Further, since image capturing up to the base of the breast is required, the radiation detector is located within the housing so that the distance between the radiation detector and the chest wall of the patient becomes suitably short during a mammography examination. Thus, the radiation detector is disposed adjacent to the front end of the housing that abuts against the chest wall of the subject. Consequently, the space between the radiation detector and the front end is narrow, and it is not possible to release sufficient heat from the radiation detector. This results in non-uniform cooling of the radiation detector, which, in turn, may reduce image capturing accuracy.